Update string in column

I am trying to update a column in a table that stores a string value using PostgreSQL. Each row would have a different string stored to it, and I am trying to append a fixed value to the column row based on a condition.

Current…

ID | STRING
-----------
01 | abcd
02 | efgh
03 | ijkl

Outcome…

ID | STRING
-----------
01 | abcd wxyz
02 | efgh wxyz
03 | ijkl wxyz

Any he开发者_开发百科lp would be greatly appreciated.